In oil or gas operations, such as drilling and/or artificial lift, a turbine may be run downhole on a tubing string to power one or more well tools. The turbine includes a rotor. Torque is imparted to the rotor when a power fluid such as, for example, a drilling fluid, is communicated to the rotor. The rotor is connected to a shaft. Torque is transferred from the rotor to the shaft during operation of the turbine. The rotor includes a plurality of blades interposed with a corresponding plurality of flow channels, through which the power fluid flows when the power fluid is communicated to the rotor. Each of the plurality of blades defines a pitch that alters the flow of the power fluid as the power fluid flows through the plurality of channels, thereby imparting torque to the rotor.
It is possible to adjust the amount of torque imparted to the rotor to accommodate overspeed or stall conditions experienced by the rotor, varying flow rates of the power fluid, and/or varying power requirements of the one or more well tools. A variable pitch rotor, which may include a motor, is sometimes used to adjust the amount of torque imparted to the rotor at a given flow rate of the power fluid. However, variable pitch rotors have a substantial number of moving parts, which parts are prone to erosion when the power fluid is communicated to the rotor. Further, variable pitch rotors can only accommodate a limited range of flow rates of the power fluid without reaching overspeed or stall conditions.
Therefore, what is needed is an apparatus, system, or method that addresses one or more of the foregoing issues, among one or more other issues.